Method and apparatus for determining top dead center in internal combustion engines

ABSTRACT

The specification discloses a novel method and apparatus for determining in an uncomparably more precise manner than was possible heretofore the top dead center in one selected cylinder of an internal combustion engine, to provide a reference point to which all of the ensuing adjustments in tuning the engine are referred. In accordance with the invention, the determination of the top dead center in the selected cylinder of an internal combustion engine is made not on the basis of movement of the piston, or pistons, or position of a journal, determination of which is being made, but on the basis of movement of the piston or position of the journal in another cylinder having set relationship to the position of the piston or journal in the selected cylinder. Generally, the relation is such that movement of the piston along the straight line is very small near the top dead center compared to the angle of crankshaft rotation, and determination of the top dead center made on the basis of such movement would be only approximate and unreliable. In accordance with the invention determination of the top dead center is made on the basis of movement of the piston in another cylinder in the position at or near the mid-stroke of the piston when the movement of the piston for the same angle of crankshaft rotation is the largest and when such movement referred to the position of the piston in the selected cylinder enables marking position of the top dead center of the piston in such selected cylinder with much greater precision. Generally, the above relationship may be compared to the sine and cosine relationship. At or near the top dead center the movement of the piston is proportional to the cosine of the angle of crankshaft rotation, and at or near the mid-stroke of the piston - proportional to the sine of such angle. Thus, determination of the top dead center in one selected cylinder resolves itself to determination of the position at or near the mid-point stroke of a piston having set relation to the position of piston in a selected cylinder, and having found that position marking the position of the piston in a selected cylinder as being precisely at the top dead center. The specification also discloses the method and apparatus for determining mid-stroke (or two-third stroke for six-cylinder engine) position of the related piston by balancing position of two adjacent pistons, one moving downwardly and one moving upwardly, both mechanically and electrically, as well as finding such positions by setting respective journals of the crankshaft accordingly.

United States Patent 191 Grikscheit et al.

[ METHOD AND APPARATUS FOR DETERMINING TOP DEAD CENTER IN INTERNAL COMBUSTION ENGINES [75] Inventors: Henry W. Grikscheit, Bloomfield;

Vernon G. Converse, III, Franklin.

both of Mich.

[73] Assignee: Scans Associates, Inc., Livonia,

Mich.

[22] Filed: May 12, 1972 [21] Appl. No.: 252,594

[52] US. Cl. 73/116, 33/180 B [51] Int. Cl. G01m 15/00 [58] Field ofSearch 73/116, 118, 119 R; 33/D1G. 15,1 PT,180 B, 180 AT, 181 AT; 324/16 T [56] References Cited UNITED STATES PATENTS 1.184.154 5/1916 Wilesmith 33/DlG. l5 3.456.50l 7/1969 Walker et al 33/180 AT X 3.691.641 9/1972 Bell et al. 33/181 AT Primary Examiner-Jerry W. Myracle Attorney, Agent, or Firm'D. Edward Dolgorukov [5 7 ABSTRACT The specification discloses a 'novel method and apparatus for determining in an uncomparably more precise manner than was possible heretofore the top dead center in one selected cylinder of an internal combustion engine, to provide a reference point to which all of the ensuing adjustments in tuning the engine are referred.

ln accordance with the invention, the determination of the top dead center in the selected cylinder of an internal combustion engine is made not on the basis of movement of the piston, or pistons, or position of a journal, determination of which is being made, but on the basis of movement of the piston or position of the 1111 3,820,386 1 June 28, 1974 journal in another cylinder having set relationship to the position of the piston or journal in the selected cylinder. Generally. the relation is such that movement of the piston along the straight line is very small near the top dead center compared to the angle of crankshaft rotation, and determination of the top dead center made on the basis of such movement would be only approximate and unreliable.

In accordance with the invention determination of the top dead center is made on the basis of movement of the piston in another cylinder in the position at or near the mid-stroke of the piston when the movement of. the piston for the same angle of crankshaft rotation is the largest and when such movement referred to the position of the piston in the selected cylinder enables marking position of the top dead center of the piston in such selected cylinder with much greater precision.

Generally, the above relationship may be compared to the sine and cosine relationship. At or near the top dead center the movement of the piston is proportional to the cosine of the angle of crankshaft rotation, and at or near the mid-stroke of the piston proportional to the sine of such angle.

Thus, determination of the top dead center in one selected cylinder resolves itself to determination of the position at or near the mid-point stroke of a piston having set relation to the position of piston in a selected cylinder,.and having found that position marking the position of the piston in a selected cylinder as being precisely at the top dead center.

The specification also discloses the method and apparatus for determining mid-stroke (or two-third stroke for six-cylinder engine) position of the related piston by balancing position of two adjacent pistons, one moving downwardly and one moving upwardly, both mechanically and electrically, as well as finding such positions by setting respective journals of the crankshaft accordingly.

20 Claims, 12 Drawing Figures PATEHTEU Jllll 28 B74 SHEURDFG This invention relates to a method of determining top dead center in a reciprocating internal combustion engine more precisely and indicating such top dead center position of one of its pistons by the marking of such position on the engine harmonic damper or other suitable place.

With the critical interest now exhibited in the automobile industry to more and more exact tuning of the engine, locating the top dead center position of a selected cylinder in the engine, usually the number one cylinder, becomes the first step of such exact tuning in order to establish a reference point to which all of the ensuing adjustments are referred.

Knowing the top dead center position of at least one piston of the engine, it is then possible to time the engine more precisely, which enhances the possibility of reducing the production of undesirable products of combustion,.such as carbon monoxide, oxides of nitrogen, unburned hydrocarbons, and others, and thereby prevent them from escaping into the atmosphere.

Top dead center is the exact geometric position at which motion of the piston in the engine cylinder reverses direction and at which combustion chamber volume is at a minimum.

Heretofore, the top dead center of the piston in the engine cylinder, usually number one cylinder, has been determined in conformity with the above definition. The spark plug of number one cylinder was taken out and a wire or a thin straight rod was inserted through the spark plug opening into the cylinderto touch the piston, and the engine was slowly rotated to cause the piston to move up and push the wire or rod upwardly. The moment the piston would stop pushing such wire or rod upwardly and come to a complete rest would indicate that the piston hasreached the top dead center, and the same was marked on the harmonic damper or was otherwise utilized.

It can be understood that as the wire or straight rod used in such determination was unavoidably moved from side to side, it greatly affected indication .of the position of top dead center, and such indication or measurement could at best be very approximate.

Obviously, such crude method of determining position of top dead center could not satisfy the presentday requirements of precision, and strenuous efforts by those skilled in the art have been exerted to find a more reliable and more precise method and apparatus for determining position of top dead center.

Applicants have come to the conclusion that determination of the top dead center position of the piston in number one cylinder cannot be made on the basis of the movement of piston in that cylinder since its movement near the top dead center position in the cylinder is very smallcompared to the movement of the journal due to the rotation of the crankshaft. The movement of the pistons in the engine may be best represented by the sine curve, and it can be seen that when the journal is near its top dead center, movements of the pistons are negligible for the same angle of crankshaft rotation, while when the journal of some other cylinder is at a known angle from the top dead center, such movement of the pistons is the greatest for the same angle of crankshaft rotation. In other words, determination of the top dead center of the piston in number one cylin- ,der should be done not at the position of number one piston near the top dead centerbut on the basis of the position of the piston in some other cylinder or cylinders, depending 'on the type of engine involved, whose journal is as close to a known angle which would represent maximum movement of that piston or pistons from the top dead center position as is possible. For example, in an eight-cylinder engine it is possible to measure from apiston whose journal is exactly from the top dead center. I

Accordingly, one of the objects of the present invention is to provide an improved method and apparatus for determining top dead center position of the piston in one cylinder of the engine, such as number one cylinder, which top dead center position is determined and marked when the piston or pistons of the engine whose journal is in the most favorable position to produce maximum movement of the head of said piston is in a position whose relationship is known to guarantee that the number one cylinder will be at its optimal top dead center position.

Another object of the invention is to provide a device to make a suitable mark when the top dead center of the piston of number one cylinder is determined.

A further object of the present invention is to provide an improved method and apparatus which determines when the two pistons of a square crankshaft engine, one moving downwardly and the other moving upwardly exactly pass each other, thereby placing the number one piston at its most optimum top dead center position.

A still further object of the invention is to provide a device in which such detennination as explained in the preceding paragraph is made electrically, mechanically or. fluidically.

A still further object of the invention is to provide a similar device which determines the positions of the pistons in a corresponding relationship to the selected top dead center cylinder in other than a square crankshaft engine, such as a six-cylinder engine.

A still further object of the present invention is to provide an improved apparatus of the foregoing nature which is simple in construction, dependable in operation, is relatively easy to use, to service and to repair.

Further objects and advantages of this invention will be apparent from the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification, wherein like reference characters designate corresponding parts in the several views.

FIG. 1 is a perspective view showing a construction of a device embodying the present invention.

FIG. 2 is a diagrammatic view of one side of a V-8 engine comparing the movement of the pistons in relation to the rotation of the crankshaft and thereby showing the advantage of setting top dead center on the basis of first setting another piston at its mid-crank position, (i.e., when the crank journal is at 90 degrees to the center line plane of the engines cylinder bore.

FIG. 3 shows a curve representing the movement of the crank journal.

FIG. 4 is a sectional elevational view showing a fixture intended for setting the journal of number two cylinder at its two-thirds stroke position in a star-shaped crankshaft commonly used in six-cylinder engines.

FIG. 5 shows the device shown in FIG. 1 set up on the engine for determining the top dead center position of the number one cylinder of a V-8 engine.

FIG. 6 is a top view of the measuring portion of the apparatus shown in FIG. 1 and 5.

FIG. 7 is an elevational view of the apparatus of FIG. 6 with the measuring devices retracted.

FIG. 8 is a sectional view taken in the direction of the arrows on the section line 8-8 of FIG. 6.

FIG. 9 is an elevational view of the control box used in this embodiment of the present invention as shown in FIGS. 1 and 5.

FIG. 10 is a schematic view of the contents of the control box of FIG. 9.

FIG. 11 is a diagrammatic view of the circuitry used in the apparatus of FIGS. 1 and 5 and others.

FIG. 12 shows the device shown in FIG. 1 set up on the engine for determining the top dead center position of the number one cylinder of an in-line six-cylinder engine.

It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways within the scope of the claims. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and not of limitation.

An examination of FIG. 2 shows that the motion of the piston for a rotation of the crankshaft through the angle 0 at the point X is much smaller than the motion of the piston for a rotation of the crankshaft through the same angle 6 at point Y. I

This can be further illustrated by the curve of FIG. 3. This is because the slope of the curve at any particular point represents the rate of change of motion of the piston at that particular point. As can be seen from an examination of FIG. 3, around point X which represents TDC (Top Dead Center) (see FIG. 2) the slope of the curve, and, therefore, the rate of change of the motion of the pistons approaches 0, which means that any change of the position of the piston at TDC (Top Dead Center) is virtually impossible to measure accurately.

However, it can also be seen that at point Y, representing the mid-crank position of the piston, the slope is at its maximum, meaning that the piston is movin fastest at this point.

It should be understood at this point, that when Applicants refer to the mid-crank position of a piston, what is meant is the position of the piston such that its corresponding crank journal is at 90 degrees to the center line plane of the engines cylinder bore. Similarly, it can be seen that when a two-thirds crank position of a piston is referred to, it is the position of the piston such that its corresponding journal is at 120 degrees to the center line plane of the engines cylinder bore.

These properties inherent in the operation of the engine manifest themselves inside the engine in a way best seen from FIG. 2. As is seen from FIG. 2, the movement of the piston 13 near its TDC position is proportional to the cosine of the angle, 0, which the crankshaftjournal 15 makes with its TDC position, while at the mid-stroke position the change in position of the piston is proportional to the sine of the same angle 0, which the journal 15 makes with the horizontal.

An examination of the chart below shows how small a change in the piston position near its TDC position is made for a certain angular displacement of the journal 15, compared to the change for the same angular displacement of the journal at the mid-crank position of the piston.

Angle change 0.0" 0.l 0.2 0.3 04 0.5 0.6

sine 0 l .0000 .0017 .0035 .0052 .0070 .0087 .0l05 Cosine 6 [.00 I00 1.00 1.00 1.00 1.00 .9999

rigid body, the journals 15 on the crankshaft are in a fixed relation to each other. On a V-8 engine having a square crankshaft they are apart. To take advantage of the fact that the motion of the pistons are easier to sense at or near this mid-crank position, Applicants essentially choose a crankshaft journal which is 90 apart from the journal corresponding to the number one piston, set the journal at its mid-stroke position, thus guaranteeing that number one piston will be at its absolute TDC position, and then mark this position in some desired fashion, such as by cutting a notch in the harmonic damper or welding a suitable pointer on the engine in the appropriate position relative to an existing notch in the harmonic damper.

This method will also work for a four-cylinder engine by marking the harmonic damper 90 from the midcrank point of the stroke.

A six-cylinder engine, the journals of which are I apart, can also be set very accurately. As shownin FIG. 3, the speed of the pistons are almost as great at the two-thirds crank position represented by letter 2 as at their mid-stroke position.

It should be understood that this invention can be used in any conventional internal combustion engine where you can use a predetermined angle from top dead center, such that the motion of the piston which is being worked on will be at its greatest, i.e. somewhere in the range where the slope of the curve, see FIG. 3, is at or near its maximum.

By setting a piston other than'the number one piston at a time when its motion is easiest to detect, Applicants can set the TDC of a selected piston much more accurately than was ever possible before, thus assuring the accurate timing of the engine, and its attendant low pollutant emission level. I

Before going on to a detailed description of the apparatus involved in the present invention, an understanding as to terminology is required.

When the cylinders of an in-line engine are referred to, the Applicants are assuming a standard in-line engine with the cylinders numbered consecutively from the front of the engine with the number one cylinder being the first cylinder, irrespective of the firing order.

When an eight-cylinder V-8 engine is referred to, Applicants are referring to the cylinders as numbered by the standard numbering arrangement with the number one cylinder being at the left front, and numbering alternately the rest of the cylinders, such that the left side of the V-8 engine would contain cylinders 1, 3, 5, and 7. Also, from time to time in the specification Applicants refer to a square crankshaft and a flat crankshaft.

A square crankshaft is one, the journals of which are 90 apart, such as in the typical V-8 engine found in the presentvday automobile.

A flat crankshaft is one, the journals of which are 180 apart, such as used in most four-cylinder engines. Although not specifically referred to, a crankshaft, the journals of which are 120 apart, is known in the art as a star shaped crankshaft.

Regardless of whether the 90, 120, or 180 measurements are referred to in the specification, it should be understood that for the purposes of this invention the reference to these measurements are the design optimums and the actual crankshafts as found in production may vary slightly from this measurement.

An apparatus for mechanically setting the journals of a six-cylinder in-line engine at its two-thirds stroke position is shown in FIG. 4. Since the three journals shown are inherently 120 apart from each other, when journal 18 is in its top dead center position, a line connecting the centers of journals 17 and 19 will be horizontal.

To set journals 17 and 19 on the same horizontal line, a hydraulic device 22 with a moveable platform 23 which is machined perpendicular to the center line of the cylinder bore 24 is used. This is used in conjunction with a test stand 27 which'holds the bottom surface 28 of the engine 29 in a fixed relationship to the cylinder bore. As the platform 23 is raised, it will come into contact with one of the journals 17 or 19 and move it until it contacts the other journal.

At this time the journals l7 and 19 will be on a horizontal line, thus assuring that journal 18 will be in its TDC position. This may then be suitably marked as the TDC position of the number one piston, since when the journal is in its TDC position, the corresponding piston,

when installed, must also be at its absolute maximum upward travel.

It should be understood that the same thing may be accomplished from the top of the bore of two selected cylinders.

- This device may also be used on a four-cylinder engine to set two journals at their 90 positions, thus assuring a journal will be at its TDC position.

Another device for mechanically setting the journal is made in the form of a fork-like member embracing the journal and setting it at its mid-crank position, or other predetermined position such that number one piston is at its TDC position.

A similar device may be built for virtually any engine, but for even greater accuracy than is possible with the mechanical setting of the crankshaft journal, Applicants prefer the balancing method, which will now be described below.

This method again takes advantage of the fact that movements of the pistons are easier to measure at their mid-crank positions than at top dead center.

Referring back to FIG. 2 which is a diagrammatic view of one side of a V-8 engine having a square crankshaft, it is seen that when the number three and number five pistons are in identical positions in their respective cylinders, the number one piston must be at top dead center. Since the journals 15 of the number three and number five pistons are 180 apart, and thus are on either side of the number one piston, these identical poportional to the linear displacement of their moveable cores.

Referring to FIGS. 5-8 and FIG. 12, in actual practice the linear transformers 31 are each mounted in an adaptor collar 32 which is, in turn, slidably mounted in a structural frame member 33 in such a manner that when the frame member is placed on the engine, the linear transformers 31 will be directly over the number three and number five pistons.

Communicating with the probe 34 of the linear transformer is a shaft 36 having a lower end 37 slidably mounted in the adaptor collar 32. The shaft has fixedly mounted on its lower end 37 by a screw 35 a bushing 38 adapted to connect the shaft 36 to a swivel member 39 by way of a screw 43.

Mounted tothe swivel member 39 by the retainer 40 and a screw 41 is a crows-foot device 42 having three downwardly radially extending legs 44. An adjusting screw 46 is provided on each leg 44 of the crows-foot 42 for purposes to be explained later.

A pin 47 keeps the crows-foot 42 from swiveling about the ball member 39. A spring 48 keeps tension on the bushing 38 to maintaintension on the measuring mechanism.

In use, the frame member 33 is placed with the aid of a handle 480 over the number three and number five cylinders of a V-8 engine and is located thereon by three locating pins 49 which fit into corresponding holes in the top surface of the engine block 52.

In the corresponding operation on a six-cylinder inline engine (see FIG. 12) the frame member 84 would be elongated to fit over the number two and number four cylinders on the engine block 85. The rest of the.

operations described below, as well as the apparatus used, will be substantially identical.

An O-ring or other appropriate seal 53 seals the enclosed space. A vacuum is applied to this space by means of a vacuum pump 54 (as shown in FIG. 5) c0nnected to the enclosed space (cylinders three and five being interconnected in the fixture.) through a suitable hose 55 and a dual-action control valve 56 communicating with the enclosed space through suitable hose connections 57 and vacuum fittings 58.

The application of the vacuum to the number three and number five pistons is important as it pulls them uniformly upward and removes the slack which would otherwise be present, thereby ensuring an accurate measurement. Applicants prefer this method rather than the use of pressure or other means because it operates on the pistons uniformly, rather than causing them to tip in the cylinder, as applying pressure would.

Since the travel of the linear transformers 31 is limited to approximately one inch and, therefore, cannot be adapted to travel the full length of the piston stroke, before the top dead center location takes place, the number three and number five pistons will have been placed approximately in their mid-crank position. It then becomes necessary to lower the linear transformer assembly previously described into close proximity with the number three and number five pistons. Since the linear transformer assembly is all mounted to the adaptor collar 32, this may be easily accomplished by providing means to raise and lower the slidably mounted collars. This is done by means of a dual-action vacuum operated cylinder 61 (as shown in FIG. 7) operatively connected to said adaptor collars by a guide 62 engaging the pins 63. Guide pins 67 keep the adaptor collars 32 in the correct relationship when acted.

upon by the cylinder 61.

The piston rod 60 is connected to the top surface of the frame member 33. When the top dead centerlocator is not in use, the piston rod 60 rests in a normally extended position as shown in FIG. 7. When it is desired to lower the crows-feet 42 into the cylinders, the two-way valve 56 is placed in the position to evacuate the enclosed space by means of the hoses 57. By virtue of the method of connecting said hoses, a vacuum will also be applied to the upper end of the cylinder 61 by the hose 59, causing the piston rod to retract into said cylinder thereby loweringboth adaptor collars 32 into the cylinder and accomplishing the purpose of lowering the crows-feet devices 42 into a position of close proximity with the top of the pistons 64.

To determine the actual top dead center of the number one piston, the engine is then slowly rotated in the pre-selected direction by any suitable means, causing the pistons 64 to move up or down, thereby causing the undercut portion 68 of the pistons 64 to contact the crows-foot devices 42 through the adjusting screws 46, causing the probes 34 of the linear transformers 31 to also move either up or down. Although the system will work without the undercut portion 68, the Applicants prefer it be done for the purpose of increasing the accuracy of the system. As the cores 34 of the linear transformers 31 are moved up and down by the movement of the pistons 64, they will give a voltage signal directly proportional to the linear displacement of the core 34 when supplied with a suitable input voltage.

In order to keep track of the two signals from the linup to zero, an adder-subtracter 72 (see FIGS. 9-11), such as the Model CEC 19-301A manufactured by Consolidated Electrodynamics Company of Bridgeport, Connecticut, is used. This device merely adds the negative voltage signal supplied from one of the linear transformers to the positive voltage signal supplied by the other linear transformer and indicates the resultant voltage signal on a digital voltmeter 73.In order to use the adder-subtracter '72 in the circuit, a device is needed to match the impedance of the signals supplied from the exciter-demodulator 65 with that of the impeear output transformers 31 and indicate when they add dance required by the adder-subtracter 72. This is performed by a voltage follower 74, such as the Model CEC 19-105, also manufactured by Consolidated Electrodynamics Company.

A suitable power supply 76 to provide the necessary current for the operation of all these devices is provided in the system and is connected to the power source through an on-off switch 77 controlling a relay 78. A pilot light 79 indicates when the power supply is operating and a fuse 80 protects the system from damage.

As with any transformer, a proper input voltage must be supplied in order to get the desired output voltage. In the case of the linear transformer 31, in order to get the desired output signal an exciter-demodulator 65, such as the Datronic Model 2018, is used. This device is w'ellknown in the art and need not be described in detail except to say that the instrument supplies a regulated excitation to th linear transformers 31. It then demodulates the signal from said linear transformers and produces a DC voltage output signal directly proportional to the displacement of the moveable core 34 of the linear transformer 31. One exciter-demodulator 65 is connected to each'of the linear transformers 31. The linear transformers 31 and the exeiter-demodulators 65 are connected in such a manner that the voltage output signal from one linear transformer will be positive and the other voltage output signal will be negative. It is seen then that when the twopistons of the engine being positioned are exactly side by side, the moveable core of each of the linear transformers if properly adjusted will also be displaced an equal amount and produce an equal voltage output signal. Since it was provided that one of said signals would be positive and one would be negative, when the moveable cores of the linear transformers are displaced an equal amount, a zero signal will result.

To make sure that the voltage output signals will be numerically equal when the cores of the linear transformers are displaced an equal amount, before use of the top dead center indicator, the structural frame member 33 is placed on a master gage block 66 (see FIG. 1). The upper surface 69 and the lower surface of the gage block 66 are machined to be parallel to each other. Therefore, assuring when the frame member 33 is placed on the upper surface 69, the distance between it and the lower surface 70 will be uniform. After the frame member 33 is placed on the gage block 66, the crows-feet 42 are lowered in the previously described manner until the adjusting screws 46 make contact with the lower surface 70. The adjusting screws 46 are adjusted to make the crows-feet 42 rest uniformly and squarely in relation to the top surface of the piston, represented by the gage block. This adjustment is repeated on each crows-foot until the adjustments are identical, then the locknut 750 is loosened and the linear transformers 31 are rotated until equal output signals are obtained, the nut 750 is then retightened and the system is ready for use.

Referring to FIG. 9, adjusting screws 71 are provided to accommodate variations in engine design. The switch 82 is for convenience in calibrating the system.

During the actual test when the top dead center indicator reads zero, this means that the voltage signals from the two linear transformers 31 have cancelled each other out. This means that the number three and number five pistons are now in their predetermined positions within their respective cylinders and by virtue of the earlier mentioned inherent geometry of the engine the number one piston must be at its absolute top dead 7 center position.

This fact may now be indicated by any suitable means, such as by cutting a notch in the harmonic damper 81 of the engine or by welding a suitable pointer to the engine in an appropriate place, opposite a previously provided notch in said damper.

When the test is completed, the two-way vacuum valve 56 is switched to its opposite position which simultaneously allows the atmosphere to re-enter the enclosed space, thereby releasing the frame member '33 from the engine and also through a suitable vacuum hose 810 applies a vacuum to the lower end of the dualaction cylinder 61, thereby causing the piston rod 60 to extend, raising the adaptor collars 32 and thereby the crows-foot assemblies 42 out of the cylinder. The frame member is then removed and the test is over.

It can be understood that the difficulty in locating the top dead center in internal combustion engine results from the fact that while the crankshaft of the engine rotates, through a short period of time at least substantially uniformly around the circular path, the pistons move reciprocally along straight lines at variable velocity, starting from rest andgradually accelerating until the piston reaches near the middle of the stroke and then decelerating until it comes to rest. In the period of time when the piston decelerates and gradually comes to a complete rest at the top dead center, the crankshaft rotates at the same speed it did while the piston was moving at its maximum velocity at the mid-crank position producing the above-explained discrepancy. Marking the top dead center when the piston approaches its point of rest is the time when the piston moves the minimum through the same degree of rotation of the crankshaft and, therefore, marking its top dead center position when the piston is at or near top dead center position would be very approximate and such marking would not satisfy the requirements for properly timing the engine. As'explained above, movement of the piston through its stroke may be taken as represented by the sine and the cosine of a certain uniform angle and the present invention is based on locating the top dead center of one selected piston not on the basis of movement of that piston but on the basis of movement of adjacent piston or pistons near the position where the piston moves the largest distance for the same angle of its crankshaft movement. Thus, substantially all the methods and apparatus disclosed above are based on the above principle.

The selection of the pistons for such movement may be done mechanically. With engines having either square or flat crankshafts, the above principle can be utilized fully. ln the six-cylinder engine, this principle is somewhat reduced in its effectiveness since the angle between adjacent journals is not 90 but 120 and, therefore, the movement of the piston at two-thirds position of its crank is moving at a somewhat reduced velocity.

Positioning of the pistons or their journals at the desired angle or position in the stroke may be done mechanically in any suitable manner and the mistake which is made in positioning the piston or its journal near the point where the piston moves faster per degree of crankshaft rotation will be very small compared to such mistakes that would occur if the piston or journal position was taken near the top dead center.

Another method of locating mid-point or two-thirds point position of the piston may be done by balancing two pistons at the same point, which would be atthe or position, at which point the basic piston, the top deadcenter position of which is being determined would be exactly in the position of top dead center and the mistake of the determination of such position would be very small. The setting of two pistons at the same position can 'be also done electrically, by the use of devices in which the distance of the movement of each piston is indicated as being proportional to the voltage produced by the electrical device, in which such distance is shown proportional to the voltage.

Thus, by abandoning the method of determining position of the top dead center on the basis of the movement of the piston the position of which is being determined, and substituting it by finding position of the top dead center on the basis of the position of the adjacent piston or pistons produces uncomparably more precise and dependable results.

We claim: I 1. The methodof determiningin a V-8 internal combustion engine having square crankshaft, the position of top dead center of the piston in number one cylinder, said method comprising sensing when the number three and the number five pistons are at the same position in their respective cylinders, and thereupon marking the position of the piston in number one cylinder as being at the top dead center.

2. The method of determining in a V-8 internal combustion engine having square crankshaft, the position of top dead center of the piston in number one cylinder, said method comprising sensing electrically when the number three and the number five pistons are at the same position in theirrespective cylinders, and thereupon marking the position of the piston in number one cylinder as being at the top dead center.

3. The method of determining in a V-8 internal combustion engine having a square crankshaft, the position of top dead center of the piston in number one cylinder, said method including applying a vacuum to the number three and number five pistons, sensing electrically when the number three and the number five pistons are at the same position in their respective cylinders while said vacuum is being applied, and thereupon marking the position of the piston in number one cylinder as being at the top dead center. I

4. The method of determining in a six-cylinder in-line internal combustion engine having a star shaped crankshaft the position of top dead center of the piston in the number one cylinder, which method comprises sensing when the number two and number four pistons are at the same positions in their respective cylinders, and marking the position of the piston in number one cylinder as being at top dead center.

5. The method of determining in a six-cylinder in-lineinternal combustion engine having a star shaped crankshaft the position of top dead center of the piston in the number one cylinder, which method comprises electrically sensing when the number two and number four pistons at the same positions in their respectivecylinders, and thereupon marking the position of the piston in number one cylinder as being at top dead center.

6. The method of determining in a six-cylinder in-line internal combustion engine having a star-shaped crankshaft, the position of top dead center of the piston in the number one cylinder, which method includes applying a vacuum to the number two and number four pistons, sensing when the number two and number four pistons are at the same positions in their respective cylinders, and thereupon marking the position of the piston in number one cylinder as being at top dead center.

7. An apparatus for determining the top dead center position of the number one piston in a V-8 internal combustion engine having a square crankshaft, said apparatus including means to slowly rotate the engine, means to measure the respective positions of the number three and number five pistons while the engine is being rotated, means to compare said measurements and to indicate when the number three and number five pistons are in identical positions, and means to mark thereupon the top dead center position of the number one piston based on the positions of the number three and number five pistons.

8. The apparatus defined in claim 7 and including a vacuum pump to apply a vacuum to the number three and number five pistons while said measurements are being taken.

9. The apparatus defined in claim 8 wherein the measuring means comprise a structural frame member adapted to be placed on and sealingly mounted over the number three and number five cylinders of a V-8 gasoline engine having a square crankshaft and thereby enclosing the number three and number five cylinders as well as a suitable working space there above, said frame member having adaptor collar assemblies slidably mounted therein directly above the number three and number five pistons of the engine, and adapted to measure the respective positions of said pistons.

10. The apparatus defined in claim 9 wherein each of said adaptor collar assemblies comprises a member with an upper and lower end, said upper end being of enlarged cross section, said member having an axially extending passageway therethrough, a linear transformer adapted to give an electrical output signal directly proportional to the linear displacement of its moveable probe adjustably mounted at the upper end of said hollow member in such a manner that said 4 probe extends into said passageway, a shaft slidably said piston contacting means include a crows-foot device with three radially downwardly extending legs, and adjusting means mounted on saidlegs at the end thereof to adjust precisely the elevations of said crowsfoot device.

13. The apparatus defined in claim 12, wherein the adjusting means are in the form of an adjustable screw on each leg of said crows-foot device.

14. The apparatus defined in claim 12 and including means to lower and hold said adaptor collar assemblies in an extended position so as to place said piston contacting means in close proximity to the pistons being measured and to simultaneously evacuate the space enclosed by said frame member, means to retract said assemblies when the measurements are done, and means to utilize the output signals of said linear transformers to indicate when the number three and number five pistons are in identical positions in their respective cylinders.

15. The apparatus defined in claim 14, wherein the indicating device comprises an exciter-dernodulator and a signal generator connected to each of said linear transformers to drive said linear transformers to produce a desired voltage output range and to have one output signal to be positive and one to be negative, an adder-subtracter to add the positive voltage signal from one linear transformer to the negative voltage signal from the other of said linear transformers, a voltage follower to match the impedance of the output signal of said linear transformers to the impedance of said adder-subtracter, and a means to indicate the result from the adder-subtracter.

16. The apparatus defined in claim 15, wherein the indicating means is in the form of a voltmeter.

' 17. The apparatus defined in claim 15, wherein the indicating means is in the form of a digital voltmeter.

18. The apparatus defined in claim 14,.wherein the lowering and evacuating means include a vacuum operated cylinder, a vacuum pump connected to said frame member and adapted to evacuate said enclosed space and also connected to said vacuum operated cylinder in such a manner as to cause simultaneous upward movement ofthe piston of said cylinder as said enclosed space is evacuated.

19. The apparatus defined'in claim 14 where said assembly retracting means includes a vacuum operated cylinder with its piston rod fixedly mounted to said frame member, said cylinder operatively connected to said collars, and a vacuum pump connected in such a manner as to cause the cylinder to move to its fully extended position and remain there until used again.

20. The apparatus defined in claim 14 wherein the lowering and retracting of said collars is performed by action valve. 

1. The method of determining in a V-8 internal combustion engine having square crankshaft, the position of top dead center of the piston in number one cylinder, said method comprising sensing when the number three and the number five pistons are at the same position in their respective cylinders, and thereupon marking the position of the piston in number one cylinder as being at the top dead center.
 2. The method of determining in a V-8 internal combustion engine having square crankshaft, the position of top dead center of the piston in number one cylinder, said method comprising sensing electrically when the number three and the number five pistons are at the same position in their respective cylinders, and thereupon marking the position of the piston in number one cylinder as being at the top dead center.
 3. The method of determining in a V-8 internal combustion engine having a square crankshaft, the position of top dead center of the piston in number one cylinder, said method including applying a vacuum to the number three and number five pistons, sensing electrically when the number three and the number five pistons Are at the same position in their respective cylinders while said vacuum is being applied, and thereupon marking the position of the piston in number one cylinder as being at the top dead center.
 4. The method of determining in a six-cylinder in-line internal combustion engine having a star shaped crankshaft the position of top dead center of the piston in the number one cylinder, which method comprises sensing when the number two and number four pistons are at the same positions in their respective cylinders, and marking the position of the piston in number one cylinder as being at top dead center.
 5. The method of determining in a six-cylinder in-line internal combustion engine having a star shaped crankshaft the position of top dead center of the piston in the number one cylinder, which method comprises electrically sensing when the number two and number four pistons at the same positions in their respective cylinders, and thereupon marking the position of the piston in number one cylinder as being at top dead center.
 6. The method of determining in a six-cylinder in-line internal combustion engine having a star-shaped crankshaft, the position of top dead center of the piston in the number one cylinder, which method includes applying a vacuum to the number two and number four pistons, sensing when the number two and number four pistons are at the same positions in their respective cylinders, and thereupon marking the position of the piston in number one cylinder as being at top dead center.
 7. An apparatus for determining the top dead center position of the number one piston in a V-8 internal combustion engine having a square crankshaft, said apparatus including means to slowly rotate the engine, means to measure the respective positions of the number three and number five pistons while the engine is being rotated, means to compare said measurements and to indicate when the number three and number five pistons are in identical positions, and means to mark thereupon the top dead center position of the number one piston based on the positions of the number three and number five pistons.
 8. The apparatus defined in claim 7 and including a vacuum pump to apply a vacuum to the number three and number five pistons while said measurements are being taken.
 9. The apparatus defined in claim 8 wherein the measuring means comprise a structural frame member adapted to be placed on and sealingly mounted over the number three and number five cylinders of a V-8 gasoline engine having a square crankshaft and thereby enclosing the number three and number five cylinders as well as a suitable working space there above, said frame member having adaptor collar assemblies slidably mounted therein directly above the number three and number five pistons of the engine, and adapted to measure the respective positions of said pistons.
 10. The apparatus defined in claim 9 wherein each of said adaptor collar assemblies comprises a member with an upper and lower end, said upper end being of enlarged cross section, said member having an axially extending passageway therethrough, a linear transformer adapted to give an electrical output signal directly proportional to the linear displacement of its moveable probe adjustably mounted at the upper end of said hollow member in such a manner that said probe extends into said passageway, a shaft slidably mounted in said passageway below and communicating with said probe, a bushing fixedly mounted on the end of said shaft, means to provide tension on said bushing, and means to contact said pistons fixedly mounted to said bushings,
 11. The apparatus defined in claim 9 wherein said tension providing means are in the form of a spring around said bushing pushing outwardly from said collar.
 12. The apparatus as defined in claim 11, wherein said piston contacting means include a crows-foot device with three radially downwardly extending legs, and adjusting means mounted on said legs at the end thereof to adjust precisely the elevations of said crows-foot device.
 13. The apparatus defined in claim 12, wherein the adjusting means are in the form of an adjustable screw on each leg of said crows-foot device.
 14. The apparatus defined in claim 12 and including means to lower and hold said adaptor collar assemblies in an extended position so as to place said piston contacting means in close proximity to the pistons being measured and to simultaneously evacuate the space enclosed by said frame member, means to retract said assemblies when the measurements are done, and means to utilize the output signals of said linear transformers to indicate when the number three and number five pistons are in identical positions in their respective cylinders.
 15. The apparatus defined in claim 14, wherein the indicating device comprises an exciter-demodulator and a signal generator connected to each of said linear transformers to drive said linear transformers to produce a desired voltage output range and to have one output signal to be positive and one to be negative, an adder-subtracter to add the positive voltage signal from one linear transformer to the negative voltage signal from the other of said linear transformers, a voltage follower to match the impedance of the output signal of said linear transformers to the impedance of said adder-subtracter, and a means to indicate the result from the adder-subtracter.
 16. The apparatus defined in claim 15, wherein the indicating means is in the form of a voltmeter.
 17. The apparatus defined in claim 15, wherein the indicating means is in the form of a digital voltmeter.
 18. The apparatus defined in claim 14, wherein the lowering and evacuating means include a vacuum operated cylinder, a vacuum pump connected to said frame member and adapted to evacuate said enclosed space and also connected to said vacuum operated cylinder in such a manner as to cause simultaneous upward movement of the piston of said cylinder as said enclosed space is evacuated.
 19. The apparatus defined in claim 14 where said assembly retracting means includes a vacuum operated cylinder with its piston rod fixedly mounted to said frame member, said cylinder operatively connected to said collars, and a vacuum pump connected in such a manner as to cause the cylinder to move to its fully extended position and remain there until used again.
 20. The apparatus defined in claim 14 wherein the lowering and retracting of said collars is performed by a single dual-action vacuum operated cylinder connected to said vacuum pump and controlled by dual-action valve. 